Implantable cardioverter defibrillator designed for use in a magnetic resonance imaging environment

ABSTRACT

An implantable cardioverter defibrillator (ICD) includes a communication interface operable to receive a communication signal from an external programmer. With the ICD not being in the presence of an MRI field generated by an MRI scanner, a communication signal is sent precharging a high energy storage capacitor before the patient undergoes the MRI scan. The signal also switches the ICD into an MRI mode which turns off the ICD&#39;s sensing functions detecting a dangerous ventricular arrhythmia. An operator monitors the patient&#39;s vital signs with sensors connected to the patient. If the patient does require the defibrillation shock, the operator sends a second communication signal delivering the defibrillation shock from the precharged high energy storage capacitor of the ICD. The patient can then be removed from the MRI scanner and the RF and gradient fields of the MRI scanner turned off.

CROSS-REFERENCE TO RELATED APPLICATIONS

This utility application is a continuation-in-part application toapplication Ser. No. 13/958,582, filed on Aug. 4, 2013, now U.S. Pat.No. 9,101,782, which is a divisional of application Ser. No. 13/589,090,filed on Aug. 18, 2012, now abandoned, which claimed priority toprovisional application 61/525,235, filed on Aug. 19, 2011.

DESCRIPTION

1. Field of the Invention

The present invention generally relates to implantable cardioverterdefibrillators. More particularly, the present invention relates to animplantable cardioverter defibrillator that can operate during medicaldiagnostic procedures such as magnetic resonant imaging.

2. Background of the Invention

Magnetic resonance imaging (MRI) is an efficient technique used in thediagnosis of many disorders, including neurological and cardiacabnormalities and other diseases. MRI has achieved prominence in boththe research and clinical arenas. It provides a non-invasive method forexamining internal body structures and functions. Because MRI has becomesuch a useful diagnostic tool, it now is used extensively in hospitalsand clinics around the world.

Magnetic resonance imaging equipment produces three main electromagneticfields during operation. In particular, MRI systems generally produceand utilize: 1) the strong static magnetic field also known as B₀ (forexample, a common 1.5 Tesla MRI scanner has over 100,000 times thestrength of the earth's magnetic field); 2) a time-varying gradientfield, Gx, Gy and Gz; and 3) a pulsed radio frequency (RF) field (knownas B1). The static field produced by most MRI systems has a magneticinduction ranging from about 0.5 to about 3.0 T. The frequency of the RFfield used for imaging is related to the magnitude of the staticmagnetic field, and, for current-generation MRI systems, the frequencyof the RF field ranges from about 6.4 to about 128 MHz. The most commonMRI system deployed and used today is 1.5 T with an RF-pulsed frequencyof 64 MHz. The time-varying gradient field is used in MRI for spatialencoding, and typically has a frequency in the Kilohertz range.

These strong electromagnetic fields produced by MRI systems can causeproblems for implantable medical devices and as a result, both the U.S.Food and Drug Administration (FDA) and many pacemaker manufacturers haveissued warnings against pacemaker recipients undergoing MRIs. Morespecifically, it has been documented that implantable cardioverterdefibrillators (ICDs) can exhibit a number of malfunctions when placedinside of a clinical MRI scanner bore. First of all, ICDs incorporate ahigh voltage power supply. This high voltage power supply converts therelatively low DC voltage from the ICD's internal battery to a highvoltage DC that is required to charge up the ICD's high energy storagecapacitor(s). Once the high energy storage capacitors of the ICD arecharged up, they can then deliver a therapeutic shock (typically in thearea of 32 to 40 joules). The internal ICD power supply (switch mode orother) does embody ferrite materials, such as a ferrite or iron coretransformer. In the presence of the main static B₀ field of the MRscanner, these ferrite or iron materials saturate and become veryinefficient. It has been documented, that the charging transformer of anICD will saturate during an MRI scan thereby making it impossible tocharge up the ICD's high energy storage capacitor to a high enoughvoltage level.

It has also been documented, that there have been cases of ICDsattempting to deliver as many as hundreds of subclinical shocks while inan MRI environment. In this case, the ICD senses a chaotic heart rhythm,however, due to the saturation of the ferrite element(s), the ICD energystorage capacitor is only charged to a relatively low voltage.Accordingly, it can only deliver low energy shocks that are generallysubclinical (below 5 joules). In fact, there have been cases of the ICDattempting to deliver so many shocks that it depletes its own batterybefore the MRI scan is even completed.

Accordingly, what is needed is a design and methodology wherein the ICDcan deliver a therapeutic cardioversion and/or defibrillation shockwhile in the presence of the MRI main static field (B₀). This isparticularly important for a patient at risk for dangerous ventriculararrhythmias. In addition, the MRI environment can be a very stressfulenvironment for many patients. Anxiety is a well documented phenomenonfor patients who become claustrophobic while placed into the relativelysmall diameter bore of the MRI scanner. These stress levels areparticularly high in so-called “closed-bore” scanners. In a high riskpatient, the chance for a dangerous arrhythmia increases when thepatient is in the MRI bore. The present invention fulfills these needsand provides other related advantages.

SUMMARY OF THE INVENTION

An exemplary embodiment of an implantable cardioverter defibrillator(ICD) is disclosed including a hermetically sealed housing and acommunication interface disposed within the housing operable to receivea communication signal from an external programmer. The communicationsignal includes a command to switch the implantable cardioverterdefibrillator from a first mode to a second mode. A processor isdisposed within the housing in electrical communication with thecommunication interface. The processor is configured to switch theimplantable cardioverter defibrillator between the first and secondmodes. A battery is disposed within the ICD housing configured toconvert chemical energy into electrical energy at a relatively low DCvoltage. A DC to AC converter is disposed within the housingelectrically coupled to the battery and configured to convert the low DCvoltage to a low AC voltage. A transformer is disposed within thehousing electrically coupled to the converter configured to convert thelow AC voltage to a high AC voltage. A rectifier is disposed within thehousing electrically coupled to the transformer and configured toconvert the high AC voltage to a high DC voltage. An energy storagecapacitor, which is used to store and deliver the necessarydefibrillation energy, is disposed within the housing electricallycoupled to the rectifier, wherein the energy storage capacitor isconfigured to store the defibrillation energy at a high DC voltage. Thedefibrillation energy may comprise at least 10 joules. A high voltageswitch is disposed within the housing electrically coupled to the energystorage capacitor. A bleed off circuit is disposed within the housingelectrically coupled to the energy storage capacitor. An optional timeris in electrical communication with the processor operable to measure aperiod of time of the second mode, wherein the processor is configuredto switch the implantable cardioverter defibrillator from the secondmode to the first mode after the period of time has elapsed and activatethe bleed off circuit to dissipate the energy. Alternately, the energymay be allowed to self discharge or bleed-off, without the use of thebleed-off or dump resistor. It is also a feature of the presentinvention that the switching from the first to the second mode and thenfrom the second mode back to the first mode can all be done by use of anexternal programmer and programming commands communicated through theICD's telemetry circuits. The second mode includes activating the DC toAC converter, transformer and rectifier to change the low DC voltage tothe high DC voltage and stored energy within the energy storagecapacitor during the period of time of the second mode. The implantablecardioverter defibrillator can now deliver a therapeutic cardioversionor defibrillation shock while in the presence of an MRI field.

In exemplary embodiments, the period of time of the second mode mayinclude more than 20 minutes. Other periods of time are possible such as30, 40, 50 or 60 minutes. The energy stored may be at least 10, 20, 30,40 or 50 joules. The amount of effective defibrillation energy storedcan vary widely based on the voltage of the capacitors, the type oftherapy being delivered, electrode location within the heart, dischargepathway resistance within the heart, etc.

In another exemplary embodiment, an additional variation of a secondarymode could be such that the defibrillator device contains a magneticfield sensor which detects the B₀ field such that in the absence of theB₀ field, the secondary mode is automatically terminated.

Another exemplary embodiment of an implantable medical device includes ahermetically sealed housing and a communication interface disposedwithin the housing operable to receive a communication signal from anexternal programmer. The communication signal includes a command toswitch the implantable medical device from a first mode to a secondmode. A processor is disposed within the housing in electricalcommunication with the communication interface. While at a suitabledistance from the MRI scanner or bore, the processor is configured toswitch the implantable medical device between the first and secondmodes. A battery is disposed within the housing to supply a low DCvoltage. A converter is disposed within the housing configured toconvert the low DC voltage to a high DC voltage. An energy storagecapacitor is disposed within the housing electrically coupled to theconverter, wherein the energy storage capacitor is configured to storethe high DC voltage at the effective defibrillation energy. The secondmode includes activating the converter to convert the low DC voltage tothe high DC voltage and storing the effective defibrillation energy inthe energy storage capacitor during a period of time of the second mode.The implantable cardioverter defibrillator can now deliver a therapeuticcardioversion or defibrillation shock while in the presence of an MRIfield.

In exemplary embodiments, the converter may include a DC to AC converterdisposed within the housing electrically coupled to the battery andconfigured to convert the low DC voltage to a low AC voltage. Theconverter may include a transformer disposed within the housingelectrically coupled to the DC to AC converter configured to convert thelow AC voltage to a high AC voltage. The converter may include arectifier disposed within the housing electrically coupled to thetransformer and configured to convert the high AC voltage to the high DCvoltage.

A high voltage switch may be disposed within the housing electricallycoupled to the energy storage capacitor.

A bleed off circuit may be disposed within the housing electricallycoupled to the energy storage capacitor. The processor may activate thebleed off circuit to dissipate the effective defibrillation energy whenswitching the second mode to the first mode. The period of time of thesecond mode may include more than 20 minutes. Alternatively, the periodof time of the second mode may include 25, 30, 35, 40, 45, 50, 55 or 60minutes.

A timer may be in electrical communication with the processor operableto measure the period of time of the second mode, wherein the processoris configured to switch the implantable medical device from the secondmode to the first mode after the period of time has elapsed.

The communication interface may be operable to receive a secondcommunication signal from an external programmer, wherein the secondcommunication signal comprises a command to switch the implantablemedical device from the second mode to the first mode.

Another exemplary embodiment of an implantable medical device includes acommunication interface operable to receive a communication signal froman external programmer, wherein the communication signal comprises acommand to switch the implantable medical device from a first mode to asecond mode. A processor is in electrical communication with thecommunication interface, the processor configured to switch theimplantable medical device between the first and second modes. A batteryis configured to supply a low DC voltage. A converter is configured toconvert the low DC voltage to a high DC voltage. A energy storagecapacitor is electrically coupled to the converter, wherein the energystorage capacitor is configured to store the effective defibrillationenergy at the high DC voltage. The second mode includes activating theconverter to convert the low DC voltage to the high DC voltage andstoring the effective defibrillation energy within the energy storagecapacitor during a period of time of the second mode.

In exemplary embodiments the converter may include a DC to AC converterelectrically coupled to the battery and configured to convert the low DCvoltage to a low AC voltage. The converter may comprise a switch modepower supply (SMPS). The converter may include a transformerelectrically coupled to the DC to AC converter configured to convert thelow AC voltage to a high AC voltage. The converter may include arectifier electrically coupled to the transformer and configured toconvert the high AC voltage to the high DC voltage.

A high voltage switch may be electrically coupled to the high energystorage capacitor.

A bleed off circuit may be electrically coupled to the high energystorage capacitor, wherein the processor activates the bleed off circuitto dissipate the remaining stored energy when switching the second modeto the first mode. The period of time of the second mode may includemore than 20 minutes.

A timer may be in electrical communication with the processor operableto measure a period of time of the second mode, wherein the processor isconfigured to switch the implantable medical device from the second modeto the first mode after the period of time has elapsed.

In another exemplary embodiment, an additional variation of a secondarymode could be such that the defibrillator device contains a magneticfield sensor which detects the B₀ field such that in the absence of theB₀ field, the secondary mode is automatically terminated.

The communication interface may be operable to receive a secondcommunication signal from an external programmer, wherein the secondcommunication signal comprises a command to switch the implantablemedical device from the second mode to the first mode.

The external programmer may include a self-contained hand-held deviceoperable to switch the implantable medical device between the first andsecond modes. The hand-held device may include a display indicating themode of the implantable medical device. The hand-held device may includea first button (or a touch screen operable icon) operable to switch theimplantable medical device from the first mode to the second mode. Thehand-held device may include a second button (or touch screen operableicon) operable to switch the implantable medical device from the secondmode to the first mode.

Another exemplary embodiment of the present invention includes a methodof performing a magnetic resonance imaging (MRI) scan on a patient withan implanted cardioverter defibrillator (ICD). The method includessending a communication signal from an external programmer to the ICDabsent a presence of an MRI field generated by an MRI scanner, thecommunication signal comprising a command to charge a energy capacitorof the ICD before the patient undergoes the MRI scan; moving the patientin close proximity to the MRI scanner; performing the MRI scan; removingthe patient from the MRI scanner when the MRI scan is completed or whenthe ICD delivers a therapy or defibrillation shock while in the presenceof the MRI field; moving the patient substantially away from the MRIfield; and allowing the ICD to either automatically bleed off, orself-discharge, the remaining stored energy in the capacitor (or aftercompleting the MRI scan, or, allowing the ICD to recharge the energycapacitor and deliver a second therapeutic charge or defibrillationshock to the patient.

The method may also include the step of monitoring the status of thepatient or ICD while performing the MRI scan, wherein monitoring thestatus of the patient may include monitoring EKG or pulse ox of thepatient.

The method may also include the step of sounding an alarm for emergencypersonnel when the ICD delivers the therapeutic charge or defibrillationshock.

Other features and advantages of the present invention will becomeapparent from the following more detailed description, when taken inconjunction with the accompanying drawings, which illustrate, by way ofexample, the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings illustrate the invention. In such drawings:

FIG. 1 illustrates a wire-formed diagram of a generic human body showingan exemplary implanted cardioverter defibrillator;

FIG. 2 illustrates a perspective view of an AIMD patient who is about tobe placed into an MRI scanner;

FIG. 3 illustrates a side view of the patient within the scanner showingan intense RF field impinging on the implanted cardioverterdefibrillator and its associated lead;

FIG. 4 illustrates a top view of the patient in the MRI scanner showingone location of the implantable cardioverter defibrillator and itsassociated lead;

FIG. 5 illustrates a pictorial view of a dual chamber cardiac pacemakerwith its associated leads and electrodes;

FIG. 6 illustrates a perspective view of a rectangular broadband orlowpass EMI filter capacitor;

FIG. 7 illustrates a horizontal section taken generally along the line7-7 of FIG. 6, illustrating the configuration of active electrode plateswithin the rectangular capacitor;

FIG. 8 illustrates a horizontal section taken generally along the lines8-8 of FIG. 6, illustrating the configuration of ground electrode plateswithin the rectangular capacitor;

FIG. 9 illustrates a perspective view showing the rectangularfeedthrough capacitor of FIG. 6 mounted to a hermetic terminal;

FIG. 10 illustrates a sectional view of the structure of FIG. 9 takengenerally along the line 10-10;

FIG. 11 illustrates a pictorial view of a prior art dual chamberimplantable cardioverter defibrillator with leads and shocking coilsimplanted into a human heart showing the complex trifurcated connectoron the quadripolar ventricular lead;

FIG. 12 illustrates a pictorial view of a state-of-the-art dual chamberimplantable defibrillator similar to FIG. 11 but now with the newin-line DF4 quadpolar connector replacing the prior cumbersometrifurcated lead based adaptor;

FIG. 13 illustrates an inside view of a first half of an implantablecardioverter defibrillator;

FIG. 14 illustrates an inside view of a second half of an implantablecardioverter defibrillator associated with the structure of FIG. 13;

FIG. 15 illustrates an electrical schematic embodying the presentinvention;

FIG. 16 illustrates a block diagram showing the steps of an embodimentof the present invention;

FIG. 17 is a depiction of a patient fitted with an ICD communicatingwith an external programmer;

FIG. 18 is a depiction of a patient fitted with an ICD communicatingwith a wand connected to an external programmer;

FIG. 19 is an illustration of a novel external programmer embodying thepresent invention;

FIG. 20 is a depiction of a patient fitted with an ICD communicatingwith the novel external programmer shown in FIG. 19;

FIG. 21 illustrates a patient inside of an MRI scanner bore; and

FIG. 22 is very similar to FIG. 19 except that an additional buttonfunction has been added to the external programmer.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Various types of active implantable medical devices are currently inuse. For example, a family of implantable hearing devices can includethe group of cochlear implants, piezoelectric sound bridge transducersand the like. Additionally, neurostimulators are used to stimulate theVagus nerve, for example, to treat epilepsy, obesity and depression.Brain stimulators are similar to a pacemaker-like device and includeelectrodes implanted deep into the brain for sensing the onset of theseizure and also providing electrical stimulation to brain tissue toprevent the seizure from actually happening. Cardiac pacemakers arewell-known in the art such as left ventricular assist devices (LVAD's),and artificial hearts, including the recently introduced artificialheart known as the Abiocor. Additionally, an entire family of drug pumpscan be used for dispensing of insulin, chemotherapy drugs, painmedications and the like. Insulin pumps are evolving from passivedevices to ones that have sensors and closed loop systems. That is, realtime monitoring of blood sugar levels will occur. These devices tend tobe more sensitive to EMI than passive pumps that have no sense circuitryor externally implanted leadwires. Additionally, implantable bone growthstimulators for rapid healing of fractures are possible along withurinary incontinence devices. Additionally, pain relief spinal cordstimulators, anti-tremor stimulators, and other types ofneurostimulators used to block pain are possible. It is also possiblefor one to have an externally worn pack. This pack could be an externalinsulin pump, an external drug pump, an external neurostimulator or evena ventricular assist device.

FIG. 1 illustrates a wire-formed diagram of a generic human body showingan exemplary implanted cardioverter defibrillator 100I. Numericaldesignation 100I includes a family of implantable cardioverterdefibrillator (ICD) devices and also includes the family of congestiveheart failure devices (CRT-D). This is also known in the art as cardioresynchronization therapy devices, otherwise known as CRT-D devices.

Referring to U.S. 2003/0050557, the contents of which are incorporatedherein by reference, metallic structures, particularly leads, aredescribed that when placed in MRI scanners, can pick up high electricalfields which results in local tissue heating. This heating tends to bemost concentrated at the ends of the electrical structure (either at theproximal or distal lead ends). A significant concern is that the distalelectrodes, which are in contact with body tissue, can cause localtissue burns.

As used herein, the lead means an implanted lead, including itsconductors and electrodes that have electrodes that are in contact withbody tissue. In general, for an active implantable medical device(AIMD), the term lead means the lead that is outside of the AIMD housingand is implanted or directed into body tissues. The term leadwire asused herein refers to the wiring or circuit traces that are generallyinside of the AIMD and are not exposed directly to body fluids.

FIG. 2 illustrates an AIMD patient 102 about to be conveyored into anMRI machine 104. Imaging processing equipment is shown as 106. Thestatic field of the MR scanner saturates ferromagnetic components withinthe ICD 100I. As will be shown, the ICD high energy storage capacitorwould be unable to charge up to a high voltage level because of thesaturation of the ICD high voltage transformer. This means the patient102 is without the benefit of the ICD 100I while in the presence of theMRI machine 104. Furthermore, the MRI machine 104 may actually cause theICD to completely deplete its battery, thereby requiring surgery toreplace the old ICD with a new ICD 100I.

FIG. 3 is a side view showing the patient 102 within the MRI scannerbore 104. An intense static B₀ field 114 is generated by the scannerscryogenic magnets. As can be seen, this static field 114 is impinging onboth the implanted cardioverter defibrillator 100I and its associatedleads 110. ICDs 100I are typically implanted in either the right or theleft part of the chest in a pectoral pocket. In some cases, they can beimplanted abdominally.

FIG. 4 is a top view of the patient 102 inside the MRI scanner bore 104.As can be seen, the ICD 100I is in a left pectoral pocket with the leads110 routed transvenously down into the interior chambers of the heart.

FIG. 5 illustrates a pictorial view of a dual chamber ICD 100I showing abipolar IS-1 lead 110 routed from the ICD 100I to a bipolar tipelectrode 118′ and anode ring electrode 120′ located inside the rightatrium. In addition, there is one of the new inline quadripolarconnectors DF4 shown routed to implanted lead 110′. Lead 110′ is routedto two high voltage shocking coils HP, 164 and HD, 166. Shocking coil HPis located in the superior vena cava while shocking coil HD is locatedin the right ventricle. Referring once again to the DF4 connector, italso has two (bipolar) low voltage lead conductors which are routed tothe bipolar electrodes 118 and 120 which are located inside of the rightventricle (RV). As can be seen, the implanted leads 110 and 110′ areexposed along their length to the intense MRI RF-pulsed field 108. Inaddition, the ICD 100I and all of its electronics are directly exposedto the MRI main static field 114. Typically, this is either 1.5 T or 3T. As previously described, this powerful main static field B₀ saturatesferrule magnetic components, such as a ferrite or iron based transformer(not shown). Referring once again to FIG. 5, one can see that there is afeedthrough capacitor-type EMI filter 140 adjacent the hermetic seal.The feedthrough capacitor 140 decouples high frequency energy, such asthe MRI RF-pulsed frequency 108 where such energy is diverted to thehousing 124 of the ICD 100I. This feedthrough capacitor is important inthe present invention in that the ICD high energy storage capacitor 140will be previously charged outside of the MRI environment. It is veryimportant that the ICD 100I not inadvertently sense the MRI RF-pulsedfield 108 as a chaotic or dangerous ventricular arrhythmia. In thiscase, if the ICD 100I falsely sensed the MRI RF or gradient field asEMI, it would inappropriately deliver the high energy shock to thepatient 102. Accordingly, proper EMI filtering is essential in thepresent invention to remove the carrier of the RF-pulsed field 108 suchthat it cannot cause inappropriate sensing. Referring once again to FIG.5, the hermetic seal assembly 132 is generally comprised of a goldbrazed alumina insulator, a glass-to-metal seal, or the like. Typically,it will have a ferrule 134 (not shown), which is laser welded directlyto the ICD housing 124. This creates a hermetic seal, which protects allICD electronic circuits from body fluid intrusion.

FIGS. 6-10 illustrate a prior art rectangular hexpolar feedthroughcapacitor (planar array) 140 mounted to the hermetic terminal 132 of anICD in accordance with U.S. Pat. No. 5,333,095 to Stevenson et al. thecontents of which are incorporated herein. As illustrated in FIGS. 6-10,in a typical broadband or lowpass EMI filter construction, a ceramicfeedthrough filter capacitor 140 is used in a hermetic feedthroughassembly 132 to suppress and decouple undesired interference or noisetransmission along one or more terminal pins 142, and may comprise acapacitor having two sets of electrode plates 144 (six active electrodeplate) and 146 (three ground electrode plates) embedded in spacedrelation within an insulative dielectric substrate or base 148, formedtypically as a ceramic monolithic structure. One set of the activeelectrode plates 144 is electrically connected at an inner diametercylindrical surface of the capacitor structure 140 to the conductiveterminal pins 142 utilized to pass the desired electrical signal orsignals. The other or second set of ground electrode plates 146 iscoupled at an outer edge surface 150 of the capacitor 140 throughmetallization to a rectangular ferrule 134 of conductive material. Inthe prior art, without regard to high frequency capacitor ESR, thenumber and dielectric thickness spacing of the electrode plate sets 144,146 varies in accordance with the capacitance value and the voltagerating of the capacitor 140.

In operation, the capacitor 140 permits passage of relatively lowfrequency electrical signals along the terminal pins 142, whileshielding and decoupling/attenuating undesired interference signals oftypically high frequency to the conductive housing 124. Feedthroughcapacitors 140 of this general type are available in unipolar (one),bipolar (two), tripolar (three), quadpolar (four), pentapolar (five),hexpolar (6) and additional lead configurations. Feedthrough capacitors140 (in both discoidal and rectangular configurations) of this generaltype are commonly employed in implantable cardiac pacemakers anddefibrillators and the like, wherein the pacemaker/ICD housing isconstructed from a biocompatible metal such as titanium alloy, which iselectrically and mechanically coupled to the hermetic terminal pinassembly which is in turn electrically coupled to the coaxialfeedthrough filter capacitor 140. As a result, the filter capacitor andterminal pin assembly prevents entrance of interference signals to theinterior of the pacemaker/ICD housing 124, wherein such interferencesignals could otherwise adversely affect the desired cardiac pacing ordefibrillation function.

FIG. 7 illustrates a horizontal section taken generally along the line7-7 of FIG. 6, illustrating the configuration of active electrode plates144 within the rectangular capacitor 140.

FIG. 8 illustrates a horizontal section taken generally along the lines8-8 of FIG. 6, illustrating the configuration of ground electrode plates146 within the rectangular capacitor 140.

FIG. 9 shows a hexpolar feedthrough capacitor 140 (which is identical tothe capacitor of FIG. 6) mounted to the hermetic terminal 132 of FIG. 5.As one can see in FIG. 9, the conductive polyimide material 152 nowconnects between the capacitor metallization 150 and the gold braze area154. The gold braze 154 forms a metallurgical bond with the titanium andprecludes any possibility of an unstable oxide forming. Gold is a noblemetal that does not oxidize and remains very stable even at elevatedtemperatures. The construction methodology illustrated in FIG. 9guarantees that the capacitor ohmic losses will remain very small at allfrequencies. By connecting the capacitor's electrode plates 146 to a lowresistivity surface such as gold, one is guaranteed that this connectionwill not substantially contribute to the capacitor's overall ESR.Keeping the ESR as low as possible is very important for diverting ahigh amount of RF current such as that induced in the lead system by MRIscanners. One is referred to U.S. Pat. No. 6,765,779 to Stevenson etal., for additional information on electrically connecting tonon-oxidized surfaces, the contents of which are incorporated herein byreference.

FIG. 10 is a cross-section of the capacitor 140 shown in FIG. 9. One cansee that the gold braze (or weld) areas 154 a and 154 b that form thehermetic seal between an alumina insulator 156 and the titanium ferrule134 are desirably on the feedthrough capacitor side. This makes it easyto manufacture the gold bond pad area 158 for convenient attachment ofthe conductive thermal-setting material 152. In other words, by havingthe gold braze hermetic seals 154 on the same side as the gold bond padarea 158, these can be co-formed in one manufacturing operation in agold braze vacuum furnace. Further, a unique thermal-setting material160 is disposed between the capacitor 140 and the underlying hermeticterminal 132. A laser weld 122 is formed continuously about the ferrule132 to form a hermetic seal to the ICD housing 124. Importantly, thislaser weld 122 also insures that the feedthrough capacitor 140 willcomprise a continuous electromagnetic shield in order to preventinterference to sensitive ICD electronic circuits.

FIG. 11 also shows a prior art outline drawing of a human heart 102 andin this case, the device 100I is a dual chamber implantable cardioverterdefibrillator. One can see that there are four connector cavities 116,116′, 118, 118′ into which the IS-1, DF-1, IS-1 and DF-1 proximalconnectors 104 a, 104 a′, 106 a, 106 a′ may be inserted. Again, thereare two implantable leads 104 and 106. Bipolar lead 104 is transvenouslyinserted into the right atrium 108 of the heart 102. It has a distal tipelectrode 104 b and a distal ring electrode 104 c. Lead 106 has fourconductors. Two of these conductors route to the distal tip electrode106 b and the distal ring electrode 106 c. The DF-1 connectors 104 a′,106 a′ are high-voltage conductors. One of the high-voltage connectors104 a′ is routed to shocking coil (HP) 128, which is generally locatedin the superior vena cava (SVC) 130 of the heart 102. The secondhigh-voltage shocking coil (HD) 132 is located in the right ventricle110. In total, there are 6 lead conductors in the system, as shown inFIG. 3.

FIG. 11 illustrates a pictorial view of an old-style prior art dualchamber implantable cardioverter defibrillator 100I with leads andshocking coils implanted into a human heart 112 showing the complextrifurcated connector 162 on the quadripolar ventricular lead. In FIG.11, one can see that there is a trifurcated lead adaptor 162 whichcombines the connectors 126 a, 128 a for the two high-voltage shockingcoils 164, 166 along with a bipolar low-voltage tip electrode 118 andring electrode 120. Referring once again to FIG. 11, one can see thatthere is also a bipolar IS-1 connector 126 a which is routed to a tipelectrode 118′ and a ring electrode 120′ in the right atrium (RA). Inthe prior art, excess lead is typically wound up in the pectoral pocket,either adjacent to or around the pacemaker/ICD and makes for a verybulky pectoral pocket lead arrangement as compared to the arrangementshown in FIG. 12. In addition the four separate connectors andassociated proximal lead segments tend to create crisscrossing tissuein-growth paths. When the ICD 100I needs to be replaced for approachingbattery end of life or any other indication, the tangle of insulatedconductor segments all tend to have tissue in-growth which makes thesurgery difficult as all of the leads must be carefully excised andseparated.

FIG. 12 illustrates a pictorial view of a state-of-the-art dual chamberimplantable defibrillator 100I similar to FIG. 11, but now with the newin-line DF4 quadripolar connector 168 replacing the prior cumbersometrifurcated lead based adaptor 162. As illustrated in FIG. 11, the dualchamber ICD 100I has both a pacing and high-voltage shocking functions.The electrode placements, both for the high-voltage shocking coils andalso the low voltage pacing sense circuits are the same as previouslydescribed for FIG. 11. However, in FIG. 12, the defibrillator 100I lead110′ incorporates the new state-of-the-art inline quadripolar DF4proximal lead connector 168 a as shown. In this case, there are now onlytwo connector cavities 168 b and 126 b in the defibrillator 100I header138. Connector cavity 126 b is a low-voltage bipolar connector cavityfor receipt of the IS-1 proximal connector 126 a. Connector cavity 168 bis a DF4 quadripolar connector cavity designed to receive the DF4proximal connector 168 a. In this case, there are still two leads 110and 110′ that are routed down into the various chambers of the heart aspreviously described in FIG. 11. When one considers the excess lead iswould up in the pacemaker pocket, one can see that the configuration inFIG. 12 is vastly superior to the trifurcated connector 134 aspreviously illustrated in FIG. 11. The surgical implant procedure isconsiderably simplified and there is a lot less bulk created in thepacemaker pocket which increases both reliability and patient comfort.

Compatibility of cardiac pacemakers, implantable defibrillators andother types of active implantable medical devices with magneticresonance imaging (MRI) and other types of hospital diagnostic equipmenthas become a major issue. If one proceeds to the websites of the majorcardiac pacemaker manufacturers in the United States, which include St.Jude Medical, Medtronic and Boston Scientific (formerly Guidant), onewill see that the use of MRI is generally contra-indicated for patientswith implanted pacemakers and cardioverter defibrillators. See alsorecent press announcements of the Medtronic Revo MRI pacemaker which wasrecently approved by the U.S. FDA. See the articles below which are allincorporated herein by reference:

-   (1) Safety Aspects of Cardiac Pacemakers in Magnetic Resonance    Imaging”, a dissertation submitted to the Swiss Federal Institute of    Technology Zurich presented by Roger Christoph Luchinger, Zurich    2002;-   (2) “1. Dielectric Properties of Biological Tissues: Literature    Survey”, by C. Gabriel, S. Gabriel and E. Cortout;-   (3) “II. Dielectric Properties of Biological Tissues: Measurements    and the Frequency Range 0 Hz to 20 GHz”, by S. Gabriel, R. W. Lau    and C. Gabriel;-   (4) “Ill. Dielectric Properties of Biological Tissues: Parametric    Models for the Dielectric Spectrum of Tissues”, by S. Gabriel, R. W.    Lau and C. Gabriel; and-   (5) “Advanced Engineering Electromagnetics, C. A. Balanis, Wiley,    1989;-   (6) Systems and Methods for Magnetic-Resonance-Guided Interventional    Procedures, Patent Application Publication US 2003/0050557, Susil    and Halperin et al., published Mar. 13, 2003;-   (7) Multifunctional Interventional Devices for MRI: A Combined    Electrophysiology/MRI Catheter, by, Robert C. Susil, Henry R.    Halperin, Christopher J. Yeung, Albert C. Lardo and Ergin Atalar,    MRI in Medicine, 2002; and-   (8) Multifunctional Interventional Devices for Use in MRI, U.S. Pat.    No. 7,844,534, Susil et al., issued Nov. 30, 2010.

However, an extensive review of the literature indicates that, despitebeing contra-indicated, MRI is indeed often used to image patients withpacemaker, neurostimulator and other active implantable medical devices(AIMDs). As such, the safety and feasibility of MRI in patients withcardiac pacemakers is an issue of gaining significance. The effects ofMRI on patients' pacemaker systems have only been analyzedretrospectively in some case reports. There are a number of papers thatindicate that MRI on new generation pacemakers can be conducted up to0.5 Tesla (T). MRI is one of medicine's most valuable diagnostic tools.MRI is, of course, extensively used for imaging, but is also used forinterventional medicine (surgery). In addition, MRI is used in real timeto guide ablation catheters, neurostimulator tips, deep brain probes andthe like. An absolute contra-indication for pacemaker or neurostimulatorpatients means that these patients are excluded from MRI. This isparticularly true of scans of the thorax and abdominal areas. Because ofMRI's incredible value as a diagnostic tool for imaging organs and otherbody tissues, many physicians simply take the risk and go ahead andperform MRI on a pacemaker patient. The literature indicates a number ofprecautions that physicians should take in this case, including limitingthe power of the MRI RF pulsed field (Specific Absorption Rate—SARlevel), programming the pacemaker to fixed or asynchronous pacing mode,and then careful reprogramming and evaluation of the pacemaker andpatient after the procedure is complete. There have been reports oflatent problems with cardiac pacemakers or other AIMDs after an MRIprocedure sometimes occurring many days later. Moreover, there are anumber of recent papers that indicate that the SAR level is not entirelypredictive of the heating that would be found in implanted leads ordevices. For example, for magnetic resonance imaging devices operatingat the same magnetic field strength and also at the same SAR level,considerable variations have been found relative to heating of implantedleads. It is speculated that SAR level alone is not a good predictor ofwhether or not an implanted device or its associated lead system willoverheat.

There are three types of electromagnetic fields used in an MRI unit. Thefirst type is the main static magnetic field designated B₀ which is usedto align protons in body tissue. The field strength varies from 0.5 to3.0 Tesla in most of the currently available MRI units in clinical use.Some of the newer MRI system fields can go as high as 4 to 5 Tesla. Atthe International Society for Magnetic Resonance in Medicine (ISMRM),which was held on 5-6 Nov. 2005, it was reported that certain researchsystems are going up as high as 11.7 Tesla. This is over 100,000 timesthe magnetic field strength of the earth. A static magnetic field caninduce powerful mechanical forces and torque on any magnetic materialsimplanted within the patient. This would include certain componentswithin the cardiac pacemaker itself and/or lead systems. It is notlikely (other than sudden system shut down) that the static MRI magneticfield can induce currents into the pacemaker lead system and hence intothe pacemaker itself. It is a basic principle of physics that a magneticfield must either be time-varying as it cuts across the conductor, orthe conductor itself must move within a specifically varying magneticfield for currents to be induced.

The second type of field produced by magnetic resonance imaging is thepulsed RF field which is generated by the body coil or head coil. Thisis used to change the energy state of the protons and elicit MRI signalsfrom tissue. The RF field is homogeneous in the central region and hastwo main components: (1) the electric field is circularly polarized inthe actual plane; and (2) the H field, sometimes generally referred toas the net magnetic field in matter, is related to the electric field byMaxwell's equations and is relatively uniform. In general, the RF fieldis switched on and off during measurements and usually has a frequencyof about 21 MHz to about 500 MHz depending upon the static magneticfield strength. The frequency of the RF pulse for hydrogen scans variesby the Lamour equation with the field strength of the main static fieldwhere: RF PULSED FREQUENCY in MHz=(42.56) (STATIC FIELD STRENGTH INTESLA). There are also phosphorous and other types of scanners whereinthe Lamour equation would be different. The present invention applies toall such scanners.

The third type of electromagnetic field is the time-varying magneticgradient fields designated B_(X), B_(Y), B_(Z), which are used forspatial localization. These change their strength along differentorientations and operating frequencies on the order of 2-5 kHz. Thevectors of the magnetic field gradients in the X, Y and Z directions areproduced by three sets of orthogonally positioned coils and are switchedon only during the measurements. In some cases, the gradient field hasbeen shown to elevate natural heart rhythms (heart beat). This is notcompletely understood, but it is a repeatable phenomenon. The gradientfield is not considered by many researchers to create any other adverseeffects.

Now turning to the present invention, these strong electromagneticfields produced by MRI systems can cause problems for implantablemedical devices and as a result, both the U.S. Food and DrugAdministration (FDA) and many pacemaker manufacturers have issuedwarnings against pacemaker recipients undergoing MRIs. Morespecifically, it has been documented that implantable cardioverterdefibrillators (ICDs) can exhibit a number of malfunctions when placedinside of a clinical MRI scanner bore. First of all, ICDs incorporate ahigh voltage power supply. This high voltage power supply converts therelatively low DC voltage from the ICD's internal battery to a highvoltage DC that is required to charge up the ICD's high energy storagecapacitor(s). Once the high energy storage capacitors of the ICD arecharged up, they can then deliver a therapeutic shock (typically in thearea of 32 to 40 joules). The internal ICD power supply (switch mode orother) does embody ferrite materials, such as a ferrite coretransformer. In the presence of the main static B₀ field of the MRscanner, these ferrite materials saturate and become very inefficient.It has been documented, that the charging transformer of an ICD willsaturate during an MRI scan thereby making it impossible to charge upthe ICD's high energy storage capacitor to a high enough voltage level.

It has also been documented, that there have been cases of ICDsattempting to deliver as many as hundreds of subclinical shocks while inan MRI environment. In this case, the ICD senses a chaotic heart rhythm,however, due to the saturation of the ferrite element(s), the ICD energystorage capacitor is only charged to a relatively low voltage.Accordingly, it can only deliver low energy shocks that are generallysubclinical (below 5 joules). In fact, there have been cases of the ICDattempting to deliver so many shocks that it depletes its own batterybefore the MRI scan is even completed.

Accordingly, the present invention embodies a design and methodologywherein the ICD can deliver a therapeutic cardioversion and/ordefibrillation shock while in the presence of the MRI main static field(B₀). This is particularly important for a patient at risk for dangerousventricular arrhythmias. In addition, the MRI environment can be a verystressful environment for many patients. Anxiety is a well documentedphenomenon for patients who become claustrophobic while placed into therelatively small diameter bore of the MRI scanner. These stress levelsare particularly high in so-called “closed-bore” scanners. In a highrisk patient, the chance for a dangerous arrhythmia increases when thepatient is in the MRI bore.

The present invention is particularly suited for use with an ICD whichemploys special input filtering such that the MRI RF pulsed field (B1)can't enter into the ICD electronics wherein electromagneticinterference (EMI) from such a field could be confused with an abnormalor dangerous ventricular arrhythmia such as ventricular fibrillation.These special filters help prevent an inappropriate ICD shock and aremore thoroughly described in U.S. Pat. No. 7,751,903; U.S. Pat. No.7,689,288 and in particular US 20100217262 (see FIG. 81 for example).

The present invention is based on ICD hardware, software and externalprogrammer modifications in order to accomplish the following sequence:

1) The ICD is especially programmed while the patient is outside of theMR scanner bore such that the ICD's high energy storage capacitor ischarged up. This is done prior to the patient entering the MRI bore sothat the ICD circuit board ferrites and power supply transformer willwork properly. The ICD is typically in a first mode, which is a modewith all of the program settings that the patient received at the timeof implant or during a follow-up visit. Prior to entering an MRI suite,the patient is to be programmed into a second mode. This is a specialMRI mode which can include many things, but in particular, it instructsthe ICD to pre-charge the energy storage capacitor while still outsidethe bore. This programming can be done by either close coupled ordistance RF prior art telemetry. In addition, a novel hand-heldprogrammer of the present invention can be used. Typically, additionalprogramming features would include turning off pacing sensor functionsand therefore have the ICD 100I pace both the ventricle via electrodes118 and 120 and the atrium via electrodes 118′ and 120′ in anasynchronous mode (typically, this would be known in the industry asVOO), meaning that asynchronous pacing pulses at a predetermined rate inpulses per minute would continue throughout the entire time that thedevice was in its second mode. This is much safer in the presence of thefields of an MRI scanner in that, rate response features are turned offto minimize EMI effects.

2) Normal prior art circuitry within the ICD to bleed off the energystorage capacitor charge after a predetermined amount of time will bemodified to allow a sufficient amount of time to complete the MRI scan.Typically the bleeder circuits will be disabled for between a 20 to 60minute time frame. The predetermined amount of time can be preset duringmanufacture of the device or adjustable by the doctor/technicianperforming the MRI scan.

There are several ways in which the device can be programmed into asecond mode and then returned to its first or normal operating mode.Three such means are (1) manually via a programmer, (2) via a timer or(3) through use of a magnetic field sensor. The first means would be touse an external programmer or hand-held device as previously describedto place the ICD from a first mode into its second or MRI mode. Theexternal programmer would similarly be used to place the ICD from thesecond mode back into the first mode. The second means would be wherethe device can be programmed with appropriate timing circuits so that itremains in an MRI mode for a specific period of time, at which time, itwill automatically bleed off the stored high voltage energy and returnto its first normal operating mode. As an alternative, the externalprogrammer can be used to switch the device into its second mode andthen at a later time, from its second operating mode back into its firstoperating mode in combination with a timer. In other words, this featurecan be either automatic or manual. The third means would be through theuse of a magnetic field sensor 218. The sensor 218 can be located withinthe ICD 100I and formed as part of the electronic circuits 130 or aspart of any other suitable electronic connection.

3) The patient will then enter the scan room and be placed in the MRIbore where the MRI scanning sequences will be performed. After thecompletion of the scans (assuming no defibrillation shock wasdelivered), the patient will be removed from the bore and the ICD energyshock capacitor may then be discharged and the ICD will be returned toits first mode normal programmed functions.

It is recognized that the patient will only be able to receive onelife-saving cardioversion/defibrillation shock during the actual MRIscan. This is because, once the energy storage capacitor is discharged,it will not be possible to recharge it in the MRI bore because of thesaturation of ferromagnetic materials (transformer) in the power supplycircuitry. However, this is far better than having an ICD patientundergo a scan wherein the ICD is incapable of delivering anylife-saving defibrillation shocks.

In a preferred embodiment, the energy storage capacitor will be chargedto the desired defibrillation therapy voltage/energy prior to theinitiation of the MRI scan. In other words, in a preferred embodiment,tiered shock therapies features will be turned off such that the patientcan only receive the maximal shock. In the prior art, it's common toattempt to cardiovert or shock a patient at a lower voltage level to seeif that lower voltage threshold will bring them back to normal sinusrhythm. One reason this is done, is that delivery of a high energy (˜36joules or higher) shock can be quite painful. However, because only oneshock is available during the MRI scan, in the preferred embodiment, thehighest energy shock available will be the preferred shock. In apreferred embodiment, the patient will be constantly monitored duringthe scan including an alarm if the ICD does deliver a high voltagetherapy shock. At this point, the scan would be immediately terminatedand the patient would be removed to a suitable distance away from thebore. Then, the ICD could, if necessary, re-charge its high energycapacitor so it could deliver additional life saving shocks ifnecessary.

Methods of placing the ICD into its “MRI mode” include: (1)reprogramming the device using an external programmer, or (2) using aspecial small programmer available to the MRI technician or radiologist(for example, a simple transmitter the size of a hand held garage doortransmitter). Additional features can be programmed into the ICD to alsoprepare it for a safe MRI scan. For example, the ICD may have pacingfunctions.

In preparation for the MR scan, in addition to charging the energystorage capacitor, the pacing function of the ICD could be programmed tofixed rate (at a higher capture level), and non-sensing to minimize thepossibility of EMI.

There are a number of patents in the prior art in which an activeimplantable medical device, such as a cardiac pacemaker is placed intoan MRI “safe-mode” wherein circuitry within the pacemaker automaticallydetects the presence of the MRI main static field. These can be Halleffect sensors, reed switches or the like. In other words, when thepacemaker detects that it's in the presence of a huge magnetic field, itwill reprogram itself typically into a fixed rate, non-sensing mode.This type of an approach will not work for the novel ICD of the presentinvention. The reason for that is, that by time the ICD detects thatit's in the main static field or the MR scanner, the power supplyferrites will already be saturated and it will be unable to charge upits own internal energy storage capacitor. This is why preprogrammingand pre-charging of the ICD's energy storage capacitor must be donebefore the patient comes in close proximity to the MRI scanner or eveninto the scan room.

FIG. 13 illustrates an inside view of a first half of an implantablecardioverter defibrillator 100I. FIG. 3 also illustrates prior artenergy storage capacitors 176. In this embodiment, they are wired inseries to achieve a relatively high voltage (˜200-800 volts). A lowvoltage battery 178 is also shown. It is not possible for the lowvoltage battery 178 to directly charge up the high voltage capacitors176. This requires a DC to AC converter or SMPS 180, a transformer 172,and high voltage charging circuits 182 to accomplish. This involves atransformer 172 with a substantial amount of ferrite material.

FIG. 14 illustrates an inside view of a second half of an implantablecardioverter defibrillator 100I associated with the structure of FIG.13. Shown are circuit boards and microprocessors 170. Also shown is thehigh voltage transformer 172 which one can see is wound around a ferriteor iron core 174. Ferromagnetic materials such as ferrite materialssaturate in the presence of the main static field B₀ of the MR scanner104 and become very inefficient. While in the presence of the mainstatic field, the transformer 172 is unable to develop enough voltage tofully charge up the energy storage capacitor 176 from the battery 178 ofthe ICD 100I. The result would be either no shock delivery orsubclinical shock clinical delivery.

FIG. 15 illustrates an electrical schematic embodying the presentinvention and is an electrical block diagram of the ICD's high voltagecharging circuitry. First of all, as previously described, there is acommunication interface 186 from an external programmer 188 to internalcircuits 130 within the ICD 100I. The external programmer 188 can beclose coupled wanded telemetry (FIG. 18) or RF distance telemetry (FIG.17). The communication interface electronics 186 and processor 130 ofthe ICD 100I can be contained on one or more circuit boards 130previously illustrated in FIG. 5. All of these circuits are typicallycontained inside the hermetically sealed housing 124 of the ICD 100I.The communication circuit 186 interfaces with a processor 130 which hasunique program functions. When the ICD 100I is switched from a firstmode and into a second (MRI) mode, by means of a signal 190 from theexternal programmer 188 to the communication interface 186, theprocessor 130 directs the DC to AC converter 180, which is typically aswitch mode power supply 180, to convert low voltage DC energy from thebattery 178 to a low voltage AC. This low voltage AC is directed to theprimary winding 194 of a transformer 172. The secondary winding 194,which has a much higher number of turns than the primary winding 192,transforms the low voltage AC to a high voltage AC. This AC voltage isthen rectified in the AC to DC rectifier 182 and the output is used tocharge the ICD's energy storage capacitor 176.

It should be noted that the high voltage storage capacitor 176 canactually consist of a number of capacitors acting either in series orparallel. For the purposes herein, it will be described as a capacitor(singular).

At this point, the energy storage capacitor 176 is fully charged and isready to deliver high voltage therapy. The capacitor 176 will remain inthis charged state until it either delivers therapeutic energy to thepatient 102 or a specific instruction may be made for a bleeder resistor196 to be switched in through bleeder switch 198 which would then bleedoff the high voltage energy and thereby discharge capacitor 176. In theMRI-ready mode, the capacitor 176 is fully charged and its high voltageelectronic switch(es) 184 are ready to deliver the energy in the highvoltage storage capacitor 176 to implanted electrodes 164, 166.

It should be noted that there is a programmable switch 200 which can usethe housing 124 of the ICD 100I as an electrode or can be switched (asshown) to a second electrode within or adjacent the human heart.Accordingly, if the ICD senses a dangerous ventricular arrhythmia, theprocessor 130 instructs switch 184 to close and thereby deliver a highvoltage life-saving shock to the patient 102. Upon completion of the MRIscanning, the ICD 100I is returned to its first or normal operatingmode, while at the same time, the bleeder 196 may be switched 198 insuch that it will bleed off the charge on the high voltage capacitor176. The ICD 100I may be returned to its original mode from a timer 202located within the processor that runs for a pre-set amount of time, bythe static magnetic field sensor, or by a second signal 190 being sentfrom the external programmer 188.

FIG. 16 illustrates a block diagram showing the steps of an embodimentof the present invention. In step 1, the patient 102 is outside the MRIscan room (or at least 10 feet from the MRI scanner bore). In step 1,the ICD 100I is programmed into its MRI mode. This can include a numberof things, but in particular, in accordance with the present invention,the energy storage capacitor 176 is fully charged up. In a preferredembodiment, the energy storage capacitor 176 is charged up to its fullcapacity. In addition, the ICD 100I has been especially designed (orsoftware programmed) such that the ICD energy storage capacitor 176 willmaintain this charge throughout the length of a typical MRI scan (˜20 to60 minutes).

In step 2, the patient 102 has entered the scan room and has beenconveyored into the MRI bore 104. In a preferred embodiment, EKGelectrodes and pulse ox monitors have been placed on the patient 102 sothat the patient 102 may be continuously monitored during the MRI scans.In particular, an external monitor is connected to the patient. Thisspecial external monitor also monitors for a high voltage shockdelivery. In the case where the ICD 100I does deliver high voltage shocktherapy, this monitor immediately triggers an alarm alerting the MRIscan technician and/or radiologist that the patient has undergone adefibrillation shock. Other preferred monitors include constant EKGmonitoring and pulse ox. The pulse ox monitors blood oxygen levels. If apatient's pulse oxygen level decrease, this is an immediate warning of adangerous ventricular arrhythmia.

Step 3 occurs if the ICD 100I did indeed deliver high voltage shocktherapy. In this case, in step 3A, the external monitors deliver analarm and the scan is immediately terminated. The patient in step 3 b isquickly removed from the MRI bore and taken at least several feet fromit (10 feet would be the preferred minimum). Then emergency personnelare summoned. The reason the patient is removed quickly from the boreand taken some distance from the bore is so the ICD and internalelectronics and in particular the high voltage charging circuit canagain operate properly. In this case, the energy storage capacitor ofthe ICD could be recharged so that one or more additional clinicalshocks could be delivered to the patient if necessary.

In the case in step 3 b, where the ICD did not deliver a shock therapyduring the MR scan, the patient is then removed from the bore 104 (at amore leisurely pace) and then the charge may be bled off the energystorage capacitor 176. In step 4 the ICD is reprogrammed to its pre-MRIconditions and settings.

In another exemplary embodiment of the present invention, there is adistinction between stored charge energy and shock delivery energy. Instep 1 the high energy storage capacitor 176 is fully charged up. Overthe length of time during an MRI procedure, the high energy storagecapacitor 176 may lose some of its initial energy. This means that thejoules delivered and the voltage delivered will be lower than when itwas fully charged before starting the MRI procedure. In exemplaryembodiments, the stored energy charge should be a minimum of 10 joulessuch that at a later time the shock delivery energy would beapproximately 5 joules or more. This means that after a period of time,for example 20-40 minutes, the high energy storage capacitor 176 canstill deliver a clinically significant energy level shock even thoughthere has been degradation and bleed-off of the stored energy. In otherexemplary embodiments, the initial stored energy charge could be upwardsof 45 joules. Also, the initial stored charge voltage could be 700-900volts or more. Therefore, during the MRI procedure the shock deliveryvoltage may be around 600-800 volts. If the voltage is too low, it maynot convert the heart 112 effectively. Other degradation and bleed-offrates may be accounted for by the present invention by those skilled inthe art as this disclosure is not limited to the specific embodimentsdisclosed herein.

Now discussing time-related voltage decay in more detail, it has beenseen through the applicant's research and development that a typicalvoltage decay of a wet tantalum capacitor stack is approximately 35percent in 60 minutes. This means that a capacitor stack charged to 765volts may decay to approximately 500 volts in an hour. Therefore, itwould be safe to generalize that in a typical device the voltage woulddrop by less than 35 percent in 40 minutes. Furthermore, it would besafe to generalize that the energy stored in a capacitor after an hourwould decay by less than 50 percent. If the capacitor stack was chargedinitially and stored 44 joules of energy (at 765 volts), in 60 minutesthe stored energy would decay to a value greater than 22 joules.Therefore, it may be generalized that the stored energy after 30-40minutes would be at least 50 percent of the initial energy. In otherwords, 44 joules would decay to a value greater than 22 joules after30-40 minutes.

Understanding that the shock delivery energy will be lower than theinitial stored charge energy due to time-related decay, the deliveredenergy to the patient for therapy will also be lessened due to losses inthe discharge process and truncation of the discharge curve. Theselosses are a function of the cycle efficiency of the capacitor. If after30-40 minutes, the capacitor has more than 22 joules of energy stored,the amount of energy actually delivered to the heart 112 for therapywill be roughly above 70 percent of the 22 joules, or greater than 15joules of energy. Therefore, for a typically implantable cardioverterdefibrillator 100I with 44 joules of stored energy in the capacitor,after 30-40 minutes the amount of energy actually delivered for therapywill be about 20 to 30 joules of energy. The present invention accountsfor these various losses and other losses not specifically describedherein, and is not limited in application to just the specific lossesdescribed.

FIG. 17 illustrates an ICD patient 102 with an implantable cardioverterdefibrillator (ICD) shown as 100I. A prior art external programmer 188is shown along with an RF distance telemetry antenna 204. RF distancetelemetry has become quite popular in recent years as opposed to the oldstyle wanded telemetry. The external programmer 188 can send and receiveelectromagnetic signals 190 to and from the implanted ICD 100I. In thiscase, the ICD 100I has its own RF telemetry transceiver and antenna (notshown). In the present invention, the ICD external programmer 188 wouldhave software modifications and perhaps hardware modifications so thatit could transmit a signal 190 which causes the ICD 100I to switchbetween a first mode and a second mode. The first mode would be itsnormal operating mode. The second mode would put it into its MRI mode,where in accordance with the present invention, the storage capacitor176 would be charged up such that it is ready to deliver an appropriatetherapeutic shock while inside of an MRI bore 104.

FIG. 18 is very similar to FIG. 17 except this illustrates the old stylewanded telemetry 206. In this case, the wand or telemetry head 206 isplaced directly over the ICD 100I. A cable 208 connects the telemetrywand 206 directly to the external programmer 188. This system iseffective, but is less convenient as it often takes a bit of time to getthe wand 206 exactly in the right position so that it will communicatewith the ICD 100I. Wanded telemetry depends upon closely coupledinductive coils, one of which is placed in the wand 206 and the otherinside or adjacent to the ICD itself. Coupling range is usually limitedto a few centimeters at best. As previously discussed in FIG. 17,close-wanded telemetry can be used to switch the ICD 100I between afirst and a second mode.

FIG. 19 illustrates a novel hand-held external programmer 210 of thepresent invention. This unit 210 is battery operated and self-containedand can also send a signal 190 to the implanted medical device 100Icausing it to switch between the first and second modes as previouslydescribed. This unit 210 is relatively inexpensive and very portablesuch that every MRI suite could have one. As previously described forFIGS. 17 and 18, the hand-held novel programmer 210 can send and receivesignals from the implanted ICD 100I. For example, while outside the MRIchamber 104, a button 212 on the hand-held external programmer 210 ispushed thereby sending a signal 190 to the ICD 100I. At that point, adigital display 214 would indicate that the MRI mode has been enabled.Then a blinking light or other indicator would come on until the energystorage capacitor 176 is fully charged up. At that time, an indicationwould come on indicating that the patient's ICD 100I is ready to bescanned and/or that the energy storage capacitor 176 is fully charged.In accordance with the present invention, the patient 102 would stay inthe second mode for a predetermined amount of time, which would requirea timing circuit 202, or in an alternative embodiment, the ICD 100Iwould stay in its second mode indefinitely until the patient 102 wasremoved from the MRI chamber and a second button 216 (or buttons) wouldbe pushed on the hand-held external programmer 210, which would causethe energy capacitor 176 to have its energy bled off and the ICD 100Ireturned to its first mode, which is its normal operating mode. It willbe obvious to those skilled in the art that the two buttons, as shown inFIG. 19, as 212 and 216 could be combined into a single toggle-typebutton, which could also switch modes.

FIG. 20 illustrates the novel programmer 210 of FIG. 19 being directedat a patient 102 transmitting electromagnetic signals 190. Thecommunication shown in FIG. 20 can be used either to place an ICD 100Iinto a second MRI mode, or upon completion of the MRI, it could be usedto return the ICD 100I to its first or normal operating mode.

The inside of an MRI scanner is a very hostile electromagneticinterference environment. There are very large amplitude RF and gradientfields that the patient is exposed to. These electromagnetic fields arealso picked up by patient implanted leads and then conducted into theinput, for example, of an implantable cardioverter defibrillator (ICD).It has been shown in previous scientific papers that ICDs haveinadvertently detected these MRI fields as a dangerous cardiacarrhythmia, such as ventricular fibrillation. This has caused ICDs toattempt to deliver a high voltage shock. Of course, while in thepresence of the MRI main static field, the ICD's high voltage chargingtransformer is saturated and is inefficient. There are even incidencesof ICDs that attempt to deliver hundreds of shocks during an MRI scan.These are subclinical shocks, in that, because of the saturation of theICD charging transformer, it is really not possible to fully charge thehigh-energy storage capacitor. There have even been cases of completeICD battery discharge during MRI scan as hundreds of subclinical shocksare delivered. It is already a feature of the present invention thatspecial EMI filters are used at the input of the ICD such thatMRI-induced electromagnetic interference is filtered out and so the ICDcan properly interpret cardiac waveforms. However, these filters are notalways completely effective and there is an alternative to this which isa manual mode of causing the pre-charged ICD to fire.

FIG. 21 illustrates a patient 102 inside of an MRI scanner bore 104. Thepatient 102 is undergoing intense RF scanning with gradient and staticfields. Also shown is a monitoring station or desk 230 at which adoctor, nurse or other medical practitioner 240 may sit or standadjacent to. Various types of monitoring equipment are attached to thepatient 102. For example, an EKG monitor 236 is shown, connected bycables 232 which would go to various skin electrodes. These wouldtypically be shielded, twisted pair cables that are protected from theintense RF fields inside the MR scanner. Also shown is a pulse oxygen(pulse-ox) monitor 238, which is connected by cable 234. This isnormally the finger clip type device that monitors pulse oxygenation bythe color under the fingernail of blood flow. Other types of monitorsmay also be employed. This allows the medical practitioner 240 toconstantly do real-time monitoring of the patient's 102 vital signs. Apacemaker programmer 188 with a remote RF telemetry antenna link 204 isalso shown as was previously described in FIG. 17. In the overall set-upas illustrated in FIG. 21, the patient's ICD high voltage energy storagecapacitor would be pre-charged in accordance with the present invention.However, the defibrillator's sensing functions would be turned off toprevent an inadvertent high voltage discharge due to confusing the MRIfield with a dangerous cardiac arrhythmia. During the real-timemonitoring, by the medical practitioner 240, if it is evident that thepatient is in hemodynamic or cardiac distress, then the medicalpractitioner 240 can immediately press a proper button sequence onremote programmer 188 instructing the ICD to immediately deliver itshigh voltage shock via the telemetry signal. At the same time, themedical practitioner 240 would instruct the MRI technician orradiologist (not shown) to immediately terminate the scan so that theycan bring the patient 102 out of the scanner 104 and out of the presenceof the main static field so that, if needed, the ICD could charge up anddeliver a second high voltage shock or even a third shock, if needed. Insummary, FIG. 21 illustrates a manual set-up wherein the patient ICD canbe pre-charged in accordance with the present invention, but can bemanually activated remotely during real-time patient monitoring duringthe MRI scan.

FIG. 22 is very similar to FIG. 19 except that an additional buttonfunction 242 has been added to external programmer 210. In anembodiment, this would have a spring-loaded cover 244 to preventinadvertent pressing of the manual high voltage delivery switch 242. Ascan be understood by those skilled in the art, there are various othermethods or devices that could be used to prevent inadvertent pressing ofthe button 242. Referring back to FIG. 21, the device 210 with themanual shock activation switch 242 could replace the pacemakerprogrammer 188, as illustrated. Alternatively, both devices 210 and 188could be utilized.

If the medical practitioner 240 did send a signal to the ICD to delivera defibrillation shock to the patient 102, an exemplary embodiment ofthe ICD can be preprogrammed to automatically enter into a non-MRI mode.This would then require that the patient be removed immediately from thestatic field such that it did not interfere with the ICD's normaloperating mode. This exemplary embodiment would allow the medicalpractitioner 240 to command the ICD to deliver a shock and then not haveto worry about manually switching the ICD into a non-MRI mode by usingthe external programmer 188/210. The ICD can then resume its normaloperating mode to determine if a second defibrillation shock is needed.

Furthermore, the external programmer 188/210 can also be configured tosend a signal to the MRI scanner to automatically turn off the RF andgradient fields when the command to the ICD to deliver thedefibrillation shock is sent. This then further simplifies the processfor the medical practitioner 240 and reduces the chance of errors. In afurther embodiment, the ICD can include sensors for the static field,such as Hall effect sensors, reed switches, MEMS-based magnetic fieldsensors and the like. Once the ICD was out of the static field byremoving the patient from the MRI, the ICD could sense this and thenenter into the ICD's normal operating mode. Again, this furthersimplified the process for the medical practitioner 240 and reduces thechance of errors.

Although several embodiments have been described in detail for purposesof illustration, various modifications may be made to each withoutdeparting from the scope and spirit of the invention. Accordingly, theinvention is not to be limited, except as by the appended claims.

What is claimed is:
 1. A method of performing a magnetic resonanceimaging (MRI) scan on a patient having an implanted cardioverterdefibrillator (ICD), the method comprising the steps of: a) determiningthat the ICD comprises a ferrite core high voltage power supplytransformer; b) with the ICD not being in the presence of an MRI fieldgenerated by an MRI scanner, sending a communication signal from anexternal programmer to the ICD, the communication signal being a commandpre-charging a high energy storage capacitor of the ICD before thepatient undergoes the MRI scan, the command also switching the ICD intoan MRI mode, the MRI mode turning off the ICD's sensing functionsdetecting a dangerous ventricular arrhythmia; connecting sensors to thepatient monitoring vital signs of the patient, the sensors displayingthe vital signs to an operator on at least one display; c) moving thepatient into the MRI scanner; d) performing the MRI scan while alsomonitoring the vital signs of the patient; e) the operator determiningfrom the display whether the patient requires a defibrillation shock; f)when the patient requires the defibrillation shock, the operator sendinga second communication signal from the external programmer to the ICD,the second communication signal being a second command delivering thedefibrillation shock from the pre-charged high energy storage capacitorof the ICD to the patient while in the presence of the MRI field; g)removing the patient from the MRI scanner after the MRI scan iscompleted or after the operator has sent the second command where theICD delivered the defibrillation shock to the patient while in thepresence of the MRI field; and h) moving the patient substantially awayfrom the MRI main static field.
 2. The method of claim 1, including thestep of the operator sending a third communication signal from theexternal programmer to the ICD, wherein the third communication signalcomprises a third command to switch the ICD to a non-MRI mode, thenon-MRI mode turning on the ICD's sensing functions detecting adangerous ventricular arrhythmia.
 3. The method of claim 2, includingthe step of if the ICD has not delivered the defibrillation shock thenallowing the ICD to automatically bleed off the charge stored in thehigh energy storage capacitor, or if the ICD has delivered thedefibrillation shock then determining that additional therapy is neededand allowing the ICD to automatically sense the dangerous ventriculararrhythmia and recharge the high energy storage capacitor andautomatically delivering a second defibrillation shock to the patient.4. The method of claim 1, wherein the second command includes switchingthe ICD to a non-MRI mode, the non-MRI mode turning on the ICD's sensingfunction detecting a dangerous ventricular arrhythmia.
 5. The method ofclaim 1, wherein the second command includes sending an MRIcommunication signal from the external programmer to the MRI scanner,where the MRI communication signal comprises a command to turn off theRF and gradient fields.
 6. The method of claim 1, wherein the ICDcomprises a magnetic field sensor in electrical communication with aprocessor for the ICD, the processor switching the ICD to a non-MRI modewhen the magnetic field sensor detects a lack of a static magneticfield, the non-MRI mode turning on the ICD's sensing function detectinga dangerous ventricular arrhythmia.
 7. The method of claim 6, includingthe step of if the ICD has not delivered the defibrillation shock thenallowing the ICD to automatically bleed off the charge stored in thehigh energy storage capacitor, or if the ICD has delivered thedefibrillation shock then determining that additional therapy is neededand allowing the ICD to automatically sense the dangerous ventriculararrhythmia and recharge the high energy storage capacitor and deliveringa second defibrillation shock to the patient.
 8. The method of claim 1,wherein the ICD comprises a magnetic field sensor in electricalcommunication with a processor for the ICD, the second command directingthe processor to switch the ICD to a non-MRI mode when the magneticfield sensor detects a lack of a static magnetic field, the non-MRI modeturning on the ICD's sensing function detecting a dangerous ventriculararrhythmia.
 9. The method of claim 8, including the step of if the ICDhas not delivered the defibrillation shock then allowing the ICD toautomatically bleed off the charge stored in the high energy storagecapacitor, or if the ICD has delivered the defibrillation shock thendetermining that additional therapy is needed and allowing the ICD toautomatically sense the dangerous ventricular arrhythmia and rechargethe high energy storage capacitor and delivering a second defibrillationshock to the patient.
 10. The method of claim 8, wherein the staticfield sensor is selected from the group consisting of a Hall effectsensor, a reed switch, and a MEMS-based magnetic field sensor.
 11. Themethod of claim 1, wherein monitoring the vital signs of the patientcomprises monitoring EKG or pulse oxygen level of the patient.
 12. Themethod of claim 1, wherein the second command includes the step ofsounding an alarm for emergency personnel.
 13. The method of claim 1,wherein the step of performing the MRI scan comprises more than 20minutes.
 14. The method of claim 1, wherein the defibrillation shock orsecond defibrillation shock comprises at least 15 joules.
 15. The methodof claim 1, wherein the defibrillation shock or second defibrillationshock comprises at least 30 joules.
 16. A method of performing amagnetic resonance imaging (MRI) scan on a patient having an implantedcardioverter defibrillator (ICD), the method comprising the steps of: a)determining that the ICD comprises a ferrite core high voltage powersupply transformer; b) with the ICD not being in the presence of an MRIfield generated by an MRI scanner, sending a communication signal froman external programmer to the ICD, the communication signal being acommand pre-charging a high energy storage capacitor of the ICD beforethe patient undergoes the MRI scan, the command also switching the ICDinto an MRI mode, the MRI mode turning off the ICD's sensing functionsdetecting a dangerous ventricular arrhythmia; c) connecting sensors tothe patient monitoring vital signs of the patient, the sensorsdisplaying the vital signs to an operator on at least one display; d)moving the patient into the MRI scanner; e) performing the MRI scanwhile also monitoring the vital signs of the patient; f) the operatordetermining from the display whether the patient requires adefibrillation shock; g) when the patient requires the defibrillationshock, the operator sending a second communication signal from theexternal programmer to the ICD, the second communication signal being asecond command delivering the defibrillation shock from the pre-charginghigh energy storage capacitor of the ICD to the patient while in thepresence of the MRI field; h) removing the patient from the MRI scannerafter the MRI scan is completed or after the operator has sent thesecond command where the ICD delivered the defibrillation shock to thepatient while in the presence of the MRI field; i) moving the patientsubstantially away from the MRI main static field; j) the operatorsending a third communication signal from the external programmer to theICD, wherein the third communication signal comprises a third command toswitch the ICD to a non-MRI mode, the non-MRI mode turning on the ICD'ssensing functions detecting a dangerous ventricular arrhythmia; and k)in the non-MRI mode if the ICD has not delivered the defibrillationshock then allowing the ICD to automatically bleed off the charge storedin the high energy storage capacitor, or in the non-MRI mode if the ICDhas delivered the defibrillation shock then determining that additionaltherapy is needed and allowing the ICD to automatically sense thedangerous ventricular arrhythmia and recharge the high energy storagecapacitor and automatically delivering a second defibrillation shock tothe patient.
 17. A method of performing a magnetic resonance imaging(MRI) scan on a patient having an implanted cardioverter defibrillator(ICD), the method comprising the steps of: a) determining that the ICDcomprises a ferrite core high voltage power supply transformer; b) withthe ICD not being in the presence of an MRI field generated by an MRIscanner, sending a communication signal from an external programmer tothe ICD, the communication signal being a command pre-charging a highenergy storage capacitor of the ICD before the patient undergoes the MRIscan, the command also switching the ICD into an MRI mode, the MRI modeturning off the ICD's sensing functions detecting a dangerousventricular arrhythmia; c) connecting sensors to the patient monitoringvital signs of the patient, the sensors displaying the vital signs to anoperator on at least one display; d) moving the patient into the MRIscanner; e) performing the MRI scan while also monitoring the vitalsigns of the patient; f) the operator determining from the displaywhether the patient requires a defibrillation shock; g) when the patientrequires the defibrillation shock, the operator sending a secondcommunication signal from the external programmer to the ICD, the secondcommunication signal being a second command delivering thedefibrillation shock from the pre-charging high energy storage capacitorof the ICD to the patient while in the presence of the MRI field, wherethe ICD comprises a magnetic field sensor in electrical communicationwith a processor for the ICD, the second command directing the processorto switch the ICD to a non-MRI mode when the magnetic field sensordetects a lack of a static magnetic field, the non-MRI mode turning onthe ICD's sensing function detecting a dangerous ventricular arrhythmia;h) removing the patient from the MRI scanner after the MRI scan iscompleted or after the operator has sent the second command where theICD delivered the defibrillation shock to the patient while in thepresence of the MRI field; and i) moving the patient substantially awayfrom the MRI main static field.
 18. The method of claim 17, includingthe step of if the ICD has not delivered the defibrillation shock thenallowing the ICD to automatically bleed off the charge stored in thehigh energy storage capacitor, or if the ICD has delivered thedefibrillation shock then determining that additional therapy is neededand allowing the ICD to automatically sense the dangerous ventriculararrhythmia and recharge the high energy storage capacitor and deliveringa second defibrillation shock to the patient.